Process and installation for producing metal tubes without welding

ABSTRACT

Metal tubes are produced in the absence of welding, by boring out a solid bar on a mandrel. This mandrel and the hollow blank left after boring is introduced into a continuous rolling mill. The mandrel is retained during the rolling operation by imposing on it a speed calculated in such a way that its available length is at least equal to that which is strictly necessary for the particular rolling operation. After the blank has been rolled, the mandrel is released in such a way that the mandrel, engaged partly in the rolled blank, stops its travel through the mill. The mandrel is removed from the rolled blank which is subjected to the further-processing stages whilst the mandrel is cooled and is then inspected, lubricated and made ready for boring another solid bar.

United States Patent [191 Lemaire et al.

PROCESS AND INSTALLATION FOR PRODUCING METAL TUBES WITHOUT WELDING Inventors: Jean Paul Lemaire, Saint Saulve;

Philippe Malicet, Valenciennes, both of France Vallourec Usines a Tubes de Lorraine-Escaut et Vallourec Reunies, Paris, France Filed: Sept. 5, 1973 Appl. No.: 394,603

Assignee:

Foreign Application Priority Data Sept. 8, 1972 France 72.31888 US. Cl. 72/209, 72/250 Int. Cl B2lb 23/00 Field of Search 72/208, 209, 96, 97, 227,

References Cited UNITED STATES PATENTS 12/1935 Diescher 72/234 X 2,063,689 12/1936 Littler 72/68 2,356,734 8/1944 Bannister 72/209 3,722,246 3/1973 Passoui 72/209 Primary ExaminerMilton S. Mehr Attorney, Agent, or FirmBreitenfeld & Levine 5 7 ABSTRACT Metal tubes are produced in the absence of welding, by boring out a solid bar on a mandrel. This mandrel and the hollow blank left after boring is introduced into a continuous rolling mill. The mandrel is retained during the rolling operation by imposing on it a speed calculated in such a way that its available length is at least equal to that which is strictly necessary for the particular rolling operation. After the blank has been rolled, the mandrel is released in such a way that the mandrel, engaged partly in the rolled blank, stops its travel through the mill. The mandrel is removed from the rolled blank which is subjected to the furtherprocessing stages whilst the mandrel is cooled and is then inspected, lubricated and made ready for boring another solid bar.

6 Claims, 2 Drawing Figures PMENTED UEE3] I974 SHEET 2 BF 2 VI V FIG.2

PROCESS AND INSTALLATION FOR PRODUCING METAL TUBES WITHOUT WELDING BACKGROUND OF INVENTION.

Non-welded metal tubes are normally manufactured by a process initially comprising two successive operations, namely boring out a solid bar coming from a heating furnace to obtain a thick, hollow blank, and subsequently rolling this blank in a mill whose successive stands are staggered by 90 and which reduces the thickness of the hollow blank in such a way that the total reduction obtained by the time the end of the mill is reached corresponds to the required tube thickness.

The boring operation is generally carried out in an oblique mill, i.e., a mill whose rolls are frustoconical and which pushes the blank onto a boring head carried by a rod held in position throughout the entire operation. In this way, the thick, hollow blank is as it were threaded onto the boring rod.

After the boring rod has been separated from the blank, the blank is positioned on an expansion bench at the input end of a continuous mill.

Hitherto, rolling has been carried out by two methods, namely free-mandrel rolling and fixed-mandrel rolling.

In the first method, a long mandrel is introduced into the hollow blank and a pusher engages the blank threaded onto its mandrel in the continuous mill. The metal rolled between the rolls and the mandrel is elongated. The mandrel is free and assumes an average speed resulting from the speeds of the metal at each stand of the continuous mill.

The combination of the mandrel and rolled blank partly covering the mandrel is collected at the output end of the mill on a mandrel-release bench where the mandrel is removed. The rolled blank continues its travel towards the further-processing stages such as, for example, heating and calibration, whilst the long mandrel is carried towards a mandrel cooler and a lubricating system to be returned to the beginning of the expansion bench.

Although in common use, this method has certain limits and disadvantages. Thus, the lengths of the rolled blanks of limited thickness are confined to around 25 metres for a diameter of 100 mm, and to around 30 metres for a blank diameter of approximately 140 mm. This limit is imposed by the collapse of the finished blank during mandrel release. In addition, the lengths to which the mandrel penetrates into the rolled blank and, hence, the mandrel-release lengths are very considerable, being of the order of 2l metres for a 25 metre rolled blank, and of the order of 26 metres for a 30 metre rolled blank. These are considerable lengths which, through the appreciable effort which they necessitate for mandrel release, promote collapse of the thin rolled blanks. Finally, since the mandrel is free during rolling, its speed is a resultant of the metal speeds in the stands in contact with the blank. Accordingly, when this number of stands in contact with the blank decreases during the discharge of the blank, the mandrel accelerates and tends to take the metal with it, producing irregularities both in the thickness .and in the diameter at the rear end of the rolled blank, known as deformations," which give rise to difficulties during mandrel-release by promoting collapse and giving rise to irregularities in the finished tube.

The second method, fixed-mandrel rolling, also comprises introducing a mandrel into the bored-out blank at the input end of a continuous mill. Although the blank/mandrel combination is pushed inside the mill, the mandrel is fixed and only travels a short distance which is generally less than the distance separating the antepenultimate stand from the last stand.

On completion of rolling, the rolled blank issues from the last stand of the mill and releases the mandrel. The mandrel is then taken back from the last cage to the beginning of the mill which it releases to enable the following blank to be brought into position.

This method also has limits and disadvantages. Thus, the working part of the mandrel is short whilst the speed of the metal in relation to that of the mandrel is high. This results in heating and excessive wear of the mandrel. In addition, this method is relatively slow because the mandrel has to be fully taken back before it can be introduced into the following blank. Finally, the same mandrel is generally used for successive blanks with the result that the mandrel cannot be properly cooled between two successive rollings.

SUMMARY OF THE INVENTION The invention relates to a new process by which it is possible in particular, in the manufacture of metal tubes in the absence of welding, to obviate the disadvantages of the prior art referred to earlier on both in regard to output and in regard to the mandrel-release operations with the resulting limits on the length of the manufactured products and the properties of the product capable of being affected by this operation.

To this end, according to the invention, a solid bar is bored out on a mandrel, after which the combination of this mandrel with the hollow blank left after boring is introduced into a continuous rnill, the mandrel is retained during the rolling operation by imposing on it a speed calculated in such a way that its available length is at least equal to that which is strictly necessary for the rolling operation in question, the mandrel is released when rolling of the blank is finished in such a way that the mandrel partly engaged in the rolled blank stops its travel through the mill, the mandrel is removed from the rolled blank, the finished blank is subjected to the usual further-processing stages whilst the mandrel is cooled, checked, lubricated and returned to the head of the installation for boring out another solid bar.

Thus, according to one of the main aspects of the invention, a blank is associated with a mandrel which acts both as a boring rod during the first stage of manufacture and as a supporting mandrel for the rolling operation in the second stage. To enable the mandrel to act as a boring rod, it has to be equipped at the beginning of the cycle with a boring head which can either remain attached to the mandrel throughout the entire cycle or can be disconnected from it at a stage in the cycle selected for its convenience and can follow its own cooling and checking cycle and can be reconnected to its mandrel or to another mandrel at any stage in the mandrel cycle.

The invention also relates to an installation for carrying out this process.

The installation according to the invention comprises a boring roll stand, a supporting stop designed to recoil and advance in the direction of the stand and to receive a mandrel equipped with a boring head; guide means arranged between the stand and the stop to support the mandrel and to prevent it from collapsing, and guide means for the tubular blank and means for ejecting the combination of the mandrel with the hollow blank when the mandrel is released from its supporting stop; a trough for axially positioning the hollow blank relative to the mandrel; a continuous mill with successive angularly staggered stands comprising, on its input duct, a system for arresting the rear of the mandrel with means regulating this arresting system during rolling to a predetermined speed and releasing the mandrel on completion of this operation; an output trough for the mill equipped with means for ejecting the rolled blank towards a mandrel-release bench; a mandrel release equipped with means for removing the rolled blank and a means for removing the mandrel; and arrangements for collecting the mandrels and carrying them back to the beginning of the installation and arrangements forv carrying the rolled blanks towards conventional further-processing installations.

The arrangements for collecting the mandrels and returning them to the beginnning of the installation can comprise a tank for cooling the mandrels, a mandrelinspection platform, a lubricatingstage, a duct for realigning the mandrels in front of the boring stand and means for delivering the mandrels to the boring stand.

The boring stand is with advantage that an oblique mill, although it should be noted that the invention can even be applied in cases where boring of the blank is carried out differently.

The advantages afforded by the invention are numerous. They relate both to the continuous rolling technique and to the boring technique, to productivity or investment and to the costs of running the installation. Thus, it is possible by using the mandrel both as a boring rod and as a rolling mandrel, to reduce the clearance between the mandrel and the hollow blank which facilitates engagement of the blank in the first stand of the continuous mill by enabling the peripheral reduction to be applied to the blank to be reduced and by reducing the-lateral bead which is formed between the rollers of the first stands of the continuous mill. In addition, the mandrel has a fixed speed rather than a speed which fluctuates during rolling so that the metaldeformation conditions in the channels are not modified through variations in the speed of the mandrel, the deformation due to this phenomenon of speed variation of the metal is eliminated in every case, it is possible to roll with stands having a more closed channel system which provides for greater uniformity of thickness in any one section, and mandrel-release is made easier through the absence of deformation and through the possibility of obtaining a more round blank by virtue of the closed channel system. Since the extent to which the mandrel penetrates into the blank is considerably lower than in free-mandrel rolling, the mandrelrelease time is shorter and it is possible to release the mandrels under optimum conditions.

In addition to the advantages which they afford in relation to the continuous rolling technique, as explained above, the process and installation according to the invention enable a high-speed borer to be used because the mandrels are immediately removed with the hollow blanks which they support. This facilitatesthe problem of cooling the boring heads which accompany the mandrels at least over part of their cycle and have all the time required for cooling.

So far as productivity is concerned, the process and installation according to the invention enable the intervals between successive borings to be reduced by half without imposing any limit upon the rolling rate as in the case in conventional installations due to the prepositioning of the mandrel and the expanding operation. Similarly, due to the fact that mandrel-release is easier because the length of mandrel to be removed is short, this mandrel-release operation, which is a delicate operation with thin blanks in conventional processes, does not slow down the production rate in any way. In addition, it is possible by virtue of the process according to'the invention to cover the entire rolling range with maximum blank lengths, which not only enables the heating furnace to be more usefully filled with solid bars, it also enables the average weight of these blanks to be increased with a reduction in the gross weight of the tubes produced.

The reduction in the length of the mandrels, the elimination of drilling rods, the reduction in the number of BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the accompanying drawing diagrammatically illustrates one embodiment of the installation according to the invention, whilst FIG. 2 is a graph comparing the relative displacements of the mandrel and the blank as a function of time in conventional continuous-rolling processes and the process according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. 1, the reference I denotes a heating furnace, such as a rotary hearth furnace, from which are removed solid bars e which, through a centring means 2, are carried to aconventional means 3 for presenting solid blanks to a boring assembly 4, such as an oblique mill, whose rolls are driven by motors 5 through elongated shafts 6. In the axis of the roll stand 4 there is a supporting stop 7 which is designed to recoil and advance in the direction of the stand and to receive a mandrel M equipped with a boring head. Diagrammatically illustrated at 8 between the stand 4 and the stop 7 are the conventional mandrel-guide means which keep the mandrel centred and prevent it from collapsing, and theconventional guide means for the tubular blank e. Through means 9 known per se, the combination of the mandrel M with the blank e can be ejected after the mandrel has been released from its supporting stop 7.

The longitudinal position of the blank e' in relation to the mandrel M is regulated in a trough l0 equipped with a feeder and an ejector.

The input trough ll of a continuous mill 12 with successive stands staggered angularly by is arranged adjacent and parallel to the positioning trough 10. At the rear'end of this trough, a system 13 is designed to arrest the rear end of the mandrel, this system being regulated during rolling to a predetermined speed by any mechanical, hydraulic or electrical means, and to release the mandrel on completion of the rolling operation.

The output trough 13' of the continuous mill is equipped with an ejecting means 14 which delivers the combination of the mandrel M with the rolled blank E in which it is partly engaged towards a mandrel-release bench 15. This bench, which comprises a mandrelrelease means, for example with a mobile die, removes the blank E towards a platform 16 and the mandrel M towards a cooling tank 17.

The rolled blanks, whose ends are cut by saws 18, are then delivered to a conventional heating furnace 19 where they are prepared for finishing.

The mandrels cooled in the tank 17 then pass onto an inspection platform 20 and are subsequently lubricated at 21 before arriving in a duct 22 in which they are realigned for the roll cage 4.

It can be seen that the mandrels M follow a cycle in the form of a single loop which passes through the boring means, the continuous rolling means and the mandrel-release means.

ln the embodiment illustrated, which would seem to be the most advantageous, the end of the mandrel which carries the boring head is opposite to that which is introduced into the continuous rolling stage. However, it would also be possible to adopt an inverse arrangement, i.e. an arrangement in which the end which carries or has carried the boring head is that which is introduced into the continuous rolling stage. The reference 23 denotes a means for separating the boring head from the mandrel, although the boring head could remain attached to the mandrel throughout the entire cycle or could be disconnected from the mandrel at any other suitable stage of the cycle followed by the mandrels.

FIG. 2 shows three graphs illustrating the movement of the blank as a function of time in solid lines and the movement of the mandrel as a function of time in broken lines, graph A relating to the free-mandrel rolling process, graph B to the fixed-mandrel rolling process and graph C to the next rolling process according to the invention.

It can be seen that process A begins with a mandrel M of considerable length which, after rolling, is engaged throughout almost the entire length of the rolled blank E,. In process B, the mandrel M is fixed and, during rolling, only travels a short distance equal at most to the distance separating the antepenultimate stand (denoted by the reference VI in the example in question) from the last stand (VIII) of the continuous mill. After the rolled blank E has left the last stand, the mandrel makes a return movement designed to enable it to engage in another hollow blank.

According to the invention, as indicated in graph C, it is sufficient to use a mandrel M which is distinctly shorter than the mandrel M, used in free-mandrel rolling. This mandrel M is kept at a constant speed during the passage of the blank through the continuous mill, after which it is released so that the combination of the mandrel M with the rolled blank E istransferred towards the mandrel-release bench and it can be seen that the mandrel M is only engaged to a limited extent in the blank E, which explains some of the advantages referred to earlier on.

It should be noted that, since the mandrel length to be removed from the rolled blank no longer constitutes a constraint, as in free-mandrel rolling, there is no reason to restrict the length of this blank to 25 or 30 metres, a limit which is imposed in practice by the prior art. For example, it is possible in a continuous mill giving a rolled blank with a diameter of 100 mm from a 3.8

m solid bar, to obtain a rolled blank 44 metres long with a mandrel 16.5 metres long. This blank, reduced on a draw-type reducer, can give a tube 300 metres long for a diameter of 21.3 mm and a thickness of 2.3

What we claim is:

1. A process for producing metal tubes without welding, comprising the steps of:

a. boring a solid bar with a mandrel, to produce a tube blank surrounding the mandrel.

b. introducing the combined blank and mandrel into a continuous mill,

c. moving the mandrel within the mill at a speed such that during the rolling operation the available length of the mandrel is at least equal to the length required for the rolling operation, but such that upon completion of the rolling operation only a small fraction of the rolled blank has the mandrel within it,

. releasing the mandrel after rolling of the blank has been completed so that the mandrel discontinues its movement through the mill,

e. removing the mandrel from the rolled blank,

f. subjecting the rolled blank to further processing,

and

g. cooling, inspecting, and lubricating the mandrel and returning it to its orginal position for boring another solid bar.

2. An installation for producing metal tubes without welding comprising a boring roller stand, a supporting stop designed to recoil and advance in the direction of the stand and to receive a mandrel equipped with a boring head; guide means arranged between the stand and the stop for supporting the mandrel and preventing it from collapsing, and guide means for the tubular blank and means for ejecting the combination of the mandrel with the hollow blank after the mandrel has been released from its supporting stop; a trough for axially positioning the hollow blank in relation to the mandrel; a continuous mill with successive angularly staggered stands comprising, on its input duct, a system for arresting the rear end of the mandrel with means regulating this arresting system during rolling to a predetermined speed and releasing the mandrel on completion of this operation such that only a small fraction of the rolled blank has the mandrel within it; a mill output trough equipped with a means for ejecting the rolled blank towards a mandrel-release bench; a mandrel-release bench equipped with means for removing the rolled blank and means for removing the mandrel; and arrangements for collecting the mandrels and carrying them back to the beginning of the installation and means for carrying the rolled blanks to conventional further-processing stages. a

3. An installation as claimed in claim 2, wherein the arrangements for collecting the mandrels and carrying them back to the beginning of the installation comprise a tank for cooling the mandrels, an inspection platform for the mandrels, a lubricating stage, a re-aligning trough in front of the boring stand and means for delivering the mandrels to the boring stand.

4. An installation as claimed in claim 3, wherein the relative arrangement of the boring mill to the continuous mill is such that the end of the mandrel which enters the continuous mill is opposite to the end which carries the boring head.

5. A process for rolling a hollow metal blank containwithin it, g l, c mprising the steps of: c. releasing the mandrel after rolling of the blank has a. introducing the combined blank and mandrel mto been completed so that the mandrerdiseeminues a continuous mill,

b. moving the mandrel within the mill at a speed such that during the o g Operation the available d. removing the mandrel from the rolled blank length of the mandrel is at least equal to the length A process as Clalmed m 9 wherem the r required f the rolling Operation, but Such that tamed mandrel advances at a constant speed during upon completion of the rolling operation only a rolling of the blanksmall fraction of the rolled blank has a mandrel 10 its movement through the mill, and 

1. A process for producing metal tubes without welding, comprising the steps of: a. boring a solid bar with a mandrel, to produce a tube blank surrounding the mandrel. b. introducing the combined blank and mandrel into a continuous mill, c. moving the mandrel within the mill at a speed such that during the rolling operation the available length of the mandrel is at least equal to the length required for the rolling operation, but such that upon completion of the rolling operation only a small fraction of the rolled blank has the mandrel within it, d. releasing the mandrel after rolling of the blank has been completed so that the mandrel discontinues its movement through the mill, e. removing the mandrel from the rolled blank, f. subjecting the rolled blank to further processing, and g. cooling, inspecting, and lubricating the mandrel and returning it to its orginal position for boring another solid bar.
 2. An installation for producing metal tubes without welding comprising a boring roller stand, a supporting stop designed to recoil and advance in the direction of the stand and to receive a mandrel equipped with a boring head; guide means arranged between the stand and the stop for suppoRting the mandrel and preventing it from collapsing, and guide means for the tubular blank and means for ejecting the combination of the mandrel with the hollow blank after the mandrel has been released from its supporting stop; a trough for axially positioning the hollow blank in relation to the mandrel; a continuous mill with successive angularly staggered stands comprising, on its input duct, a system for arresting the rear end of the mandrel with means regulating this arresting system during rolling to a predetermined speed and releasing the mandrel on completion of this operation such that only a small fraction of the rolled blank has the mandrel within it; a mill output trough equipped with a means for ejecting the rolled blank towards a mandrel-release bench; a mandrel-release bench equipped with means for removing the rolled blank and means for removing the mandrel; and arrangements for collecting the mandrels and carrying them back to the beginning of the installation and means for carrying the rolled blanks to conventional further-processing stages.
 3. An installation as claimed in claim 2, wherein the arrangements for collecting the mandrels and carrying them back to the beginning of the installation comprise a tank for cooling the mandrels, an inspection platform for the mandrels, a lubricating stage, a re-aligning trough in front of the boring stand and means for delivering the mandrels to the boring stand.
 4. An installation as claimed in claim 3, wherein the relative arrangement of the boring mill to the continuous mill is such that the end of the mandrel which enters the continuous mill is opposite to the end which carries the boring head.
 5. A process for rolling a hollow metal blank containing a mandrel, comprising the steps of: a. introducing the combined blank and mandrel into a continuous mill, b. moving the mandrel within the mill at a speed such that during the rolling operation the available length of the mandrel is at least equal to the length required for the rolling operation, but such that upon completion of the rolling operation only a small fraction of the rolled blank has a mandrel within it, c. releasing the mandrel after rolling of the blank has been completed so that the mandrel discontinues its movement through the mill, and d. removing the mandrel from the rolled blank.
 6. A process as claimed in claim 5, wherein the retained mandrel advances at a constant speed during rolling of the blank. 